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混凝土是由多种材料组成的非匀质人造石材。其结构组成为固相、液相和气相,具有弹一粘一塑性及各向异性等特点。各相之间声学特性阻抗差异很大,声波通过混凝土时,在各相界面上产生反射和散射,造成较大的散射衰减。由于混凝土的粘塑性作用,对声能有较大的粘滞性吸收。所以,对超声波来说,混凝土就像个滤波器,由发射换能器所发出的超声波,经过混凝土介质传递后,声波的相频和幅频均会发生变化,混凝土对声波的这种特性可视为滤波特性。这种滤波特性直接与混凝土的内部结构组成及其物理性能有关,在其组成材料及各因素均相
Concrete is a non-homogeneous artificial stone composed of a variety of materials. Its structural composition is solid phase, liquid phase and gas phase, with the characteristics of elasticity, stickiness, plasticity and anisotropy. The acoustic impedance between the phases is very different. When the sound waves pass through the concrete, reflections and scattering occur at the interfaces of the phases, causing large scattering attenuation. Due to the viscoplastic effect of concrete, there is a greater viscous absorption of acoustic energy. So, for ultrasonics, the concrete acts like a filter. After the ultrasonic waves emitted by the transmitting transducer pass through the concrete medium, the phase frequency and the amplitude and frequency of the acoustic wave will change. This characteristic of the acoustic wave of concrete can be Treated as filter characteristics. This filtering characteristic is directly related to the internal structure of the concrete and its physical properties, and its constituent materials and all factors are homogeneous.